A large portion of today's internet traffic goes through content delivery networks which provide a limited set of data to a large number of destinations. These technologies generally rely on caching and replication. Replication allows content delivery networks to provide the same data to multiple destinations. Typically, content delivery networks perform replication through IP multicast communications or overlay networks. IP multicast enables replication by allowing the data to be sent to all end-hosts. Unfortunately, IP multicast retransmissions can be significantly inefficient, as IP multicast lacks a mechanism for limiting the data transmitted during a retransmission to an arbitrary set of end-hosts. By contrast, overlay networks can greatly simplify replication. However, overlay networks require a significant amount of state to be maintained by intermediate nodes, which can become onerous
More recently, a new multicast paradigm called bit indexed explicit replication (BIER) has emerged. Contrary to native IP multicast, BIER allows for data to be transmitted to an arbitrary set of end-hosts, which can be defined by a group of bits representing a selected set of end-hosts. However, BIER has limited efficiency and reliability, and lacks end-to-end flow control as well as backwards compatibility with connection-oriented transport layer protocols and communications.